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Arches

National Park

Utah

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park geology subheading
photo of sandstone formation at Arches National Park
Arches National Park, Utah

Southeast Utah consists of numerous red rock canyons carved into layers of sedimentary rock formations that have been molded and eroded by a variety of uplifting and erosional processes. The geologic strata exposed in Arches and Canyonlands range from the Paradox Formation (Pennsylvanian Period) to the Mancos Shale Formation (Cretaceous Period). These formations consist of many intermixed layers of marine, freshwater and eolian deposition that are collectively several thousand feet thick. Regionally, these depositional layers are nearly horizontal with a slight dip to the north (Berghoff and Vana-Miller, 1997). The area is an erosional landscape with over a quarter of the area being exposed bedrock. Erosional processes can impact water resources, and do so in these two parks. For example, sediments and evaporites from the Paradox Formation cause dissolved solids levels to increase significantly (thousands of milligrams per liter) in local waters. Ground water encountered in formations below the Carmel Formation can typically be high in sulfates (Hand, 1979). The soils vary widely on the Colorado Plateau and typically reflect the parent material from which they are derived. Vegetation boundaries are usually abrupt, corresponding to sharp changes in substrate or available soil moisture. Soils located in the lower elevations and canyon floors are typically hot and dry, and are poorly developed, while those at higher elevations are cool and moist. Soils found in recent eolian deposits, derived from sandstone, range from sandy loam to sand . Those derived from shale parent material range from clay loam to clay. Deeper soils are found in the valley alluvial fills, whereas shallow soils and exposed sandstone are found on rims, benches, and slopes associated with anticlines and synclines (Lammars, 1991). Overgrazing by livestock has led to an increase in precipitation, runoff and erosion of soils. Vast changes in plant cover and composition have been the result, as have the downcutting of streams and loss of the A-horizon from the soil profile (Barth and McCullough, 1988). These changes have made it easier for exotic species to be introduced and flourish. Knopf and Cannon (1981) found that willow is often slow to recover following overgrazing and, Kennedy (1977) reported that complete conversion of the vegetative is the result of grazing in some western areas of the United States. Since these systems alterations are often slow to recover in an arid environment, and the changes can be so drastic, management techniques in many cases do not work, except for the sometimes costly and difficult task of removing the problem that caused the initial impact.

Many of the geologic formations in the region were deposited in marine environments and therefore have a naturally high concentration of dissolved solids. Energy resource development for coal, oil and gas, and oil shale can contribute to the salt loading problem. Fossil fuels are generally located in association with marine shales and extraction of these resources results in increased levels of dissolved minerals in the water. Increased salinity can be caused by leaching of spoils material, discharge of saline ground water, and increased erosion from surface disturbances. Total dissolved solids from mining spoils leachate have been recorded as high as 3900 mg/L in northwestern Colorado (Parker and Norris, 1983). In addition to fossil fuel extraction, there has been a substantial amount of uranium mining in areas surrounding the National Park Service lands on the Colorado Plateau. Surface runoff and pollution from uranium mines can result in elevated levels of heavy metals, radionuclides and other toxic elements.

Arches National Park Ground Water

Arches is in the southeastern part of the Salt Valley anticline. The Salt Valley now occupies the crest of the Salt Valley anticline as a result of breaching and erosion (Sumsion, 1971). Specifically, in recent geologic history, ground waters that moved through the near-surface rocks, encountered the salt masses left as a result of resistance to the pressure of overburden and concomitant salt flow during the Middle Pennsylvanian through the Jurassic period. The ground water dissolved the salt from the upper structures, leaving less soluble gypsum behind. The volume of salt near the surface has thus been reduced. The elongate valleys (23 miles long, 37 kilometers) such as Salt Wash in Arches resulted from overlying strata collapsing into the elongate crests of these salt features (Baars, 1972). Exposed on the limbs of the anticline are the Wingate

Sandstone of the Triassic period (210 million years ago), the Navajo Sandstone of the Triassic and Jurassic (145 million years ago) periods, and the Entrada Sandstone of the Jurassic period. Other formations in the park range in geologic age from the Pennsylvanian (285 million years ago) to Cretaceous (65 million years ago); these formations are dry due to very low transmissivity which retards recharge or they contain unpotable water unlike many other formations which can support aquifers if the right hydrologic conditions exist. Typically, wells associated with the Navajo, Entrada, or Wingate formations provide water through fractures or joints. The initial supply of water to these formations is through percolation down through permeable layers of rock and through these joints and fractures. In the late 1950's and early 60's, Arches' staff sought information on a replacement drinking water source at Arches Headquarters and a potable water source at the Devil's Garden campsite At that time park staff hauled water into the campsite from the park headquarters, 12 miles to the south. Price (1959) , Arnow (1963) and Sumsion (1971) summarized attempts to locate potable water sources at three different areas within Arches. Water quality data from these studies are presented in Tables 2a and 2b. Engineers located water at approximately 86 feet (26 meters) at the park headquarters according to price (1959). The final well depth was 123.4 feet (37.6 meters), and the entire length of the well remained in the Navajo Sandstone. The water quality data for the replacement headquarters well revealed hard water (224 ppm as CaCO3) and high specific conductance (762 µmhos). Arnow (1963) described a weel drilled into the Navajo Sandstone in the Devil's garden area of Arches. The well depth totaled 900 feet, and engineers encountered water at 745 feet (227 meters) in the Wingate formation. The maximum yield for this well was 4 gallons per minute (gpm). Arnow (1963) noted that additional water could be sought by developing one or more of the springs, or by drilling in the Navajo Sandstone one mile northeast of Devil's Garden. Numerous springs and seeps emanate from the contact between the Dewey Bridge member, a less permeable rock, and the Slick Rock Member of the Entrada Sandstone. An operable well now exists at Devil's Garden Campground.

Sumsion (1971) reports on the hydrologic investigations of the Willow Flats area for a potential water source in the Navajo Sandstone. He estimated that this formation would provide 50 to 56 gallons per minute (gpm)of water, and that the water would move through fractures. This information is based on a soil boring hole drilled in 1969 approximately 1.5 miles to the west of the proposed test area. The driller reported a yield of 56 gpm of water at a depth of 1,570 feet (479 meters) at the base of the Navajo Sandstone. Eight springs in the western portion of the park near Herdina Park were tested for quality, all of which were potable. A ninth spring, called Winter Camp Spring near the Turnbow Cabin, and emanating from the Summerville Formation, was unpotable as a result of total dissolved solids equaling 5,560 mg/L. Further the Winter Camp Spring water contains high sulfate levels at 306 ppm (Table 2b). These springs are actually seepage sites in the Entrada Sandstone for the most part, because the channel is eroded below the water table.

Perennial and Ephemeral Streams

A large number of canyons on the Colorado Plateau do not carry perennial waters, but instead are ephemeral in nature. These channels lead to the Green and Colorado rivers and were formed by fluvial processes. During storm events, these channels can carry large amounts of water and debris. Remembering the destructive power of these flash floods is important when considering development is proposed in associated flood plains (Berghoff and Vana-Miller, 1997). In addition, these floods can carry a tremendous amount of sediment contributing to a water quality problem albeit a naturally induced one. Certain activities within the parks may exacerbate sedimentation problems; these include trampling and removal of vegetation, use of four 4-wheel drive vehicles and trespass cattle.

There are only three perennial streams within Canyonlands - the Colorado and Green rivers and Salt Creek. Documented flows in Salt Creek range from 0.448 to 0.896 cubic feet/second (cfs) (Long and Smith, 1996). The creek commences on Bureau of land Managment land and flows north to the park. Several issues regarding this water resource and the surrounding area are discussed thoroughly in the issues section of this report. Other perennial streams located in Arches are Salt Wash and Courthouse Wash. Flows for Salt Wash range from 0.25 to 1.4 cfs, and a one time measurement for Courthouse Wash was 0.1 cfs (Long and Smith, 1996). All of these systems depend on spring source water as well as precipitation to drive fluvial processes.

Mining: From Atlas to Potash

Atlas Corporation Moab Mill Site An overwhelming concern of both parks is the remediation efforts of Atlas Corporation Moab Mill, a now decommissioned uranium mill site. The mill site and associated tailings are located on the northwest bank of the Colorado River southeast of Arches headquarters, and 1.9 miles (5 kilometers) northwest of Moab. The site totals 400 acres (162 hectares) comprised of a processing facility, tailings pond and pile. The 10.5 million ton (9.5 million metric ton) pile covers some 130 acres (52.6 hectares). Atlas Corporation submitted an amendment to its existing Nuclear Regulatory Commission License No. SUA-917 requesting that Atlas be allowed to 1) reclaim and stabilize the tailings pile for permanent disposal at its present location near Moab, 2) discontinue its responsibility for the tailings, and 3) prepare the 400 acre site for closure (US Nuclear Regulatory Commission, 1996a). A draft and technical evaluation of Atlas' remediation plan raise additional questions about ground water contamination (US Nuclear Regulatory Commission, 1996b, 1997).

The National Park Service's major concern is an elevated ammonia level in the Colorado River downstream of the pile. The U.S. Fish and Wildlife Service issued a jeopardy opinion in reference to the remediation plan as a result of the elevated ammonia level (Irwin, R., 1997 pers. Comm., National Park Service). Ammonium levels of 2400 mg/L were measured in the tailings fluid in 1987 (U.S. Nuclear Regulatory Commission, 1997). At a pH of 8.0 and a water temperature of 10°C, a total ammonia level of 5.86 mg/L can be toxic to fish. Ground water at the background monitoring site AMM-1 established in 1988 was generally a sodium/chloride type, whereas the tailing fluids are a sodium-magnesium/sulfate type water. Sulfate is the dominant anion of the tailing fluid and apparently does influence the ground water at a well to the south. The Nuclear Regulatory Commission questions whether the AMM-1 site was a suitable background monitoring well, because of its close proximity to an old ore storage pad (U.S. Nuclear Regulatory Commission, 1997).

Generally, the shallow alluvial ground water flow is from northwest to southeast towards the Colorado River; however, flow directions and gradients are likely to be variable throughout the year due to stage influences of the Colorado River. During much of the year, shallow and deep monitoring wells in the alluvium show that ground water elevations are above the river stage, demonstrating that the river is gaining flow from the ground water, however, during spring runoff, the river stage exceeds the ground water elevation in the wells, thus the river contributes flow to the alluvial ground water during this period (U.S. Nuclear Regulatory Commission, 1997).

Arches, Canyonlands, and the Water Resources Division of the National Park Service continue to work closely with Atlas Corporation and the Nuclear Regulatory Commission on an acceptable remediation plan for the Atlas Corporation Mill Site.

Dolores Mining District

Upstream approximately, 20 miles from Moab, the Dolores River joins the Colorado River This confluence is significant because uranium tailings remediation of the Uravan mill site is located approximately 50 river miles away from the Colorado River near Moab. Umetco Minerals Corporation, a division of Union Carbide, has supervised the reclamation of the Uravan Mill Site since 1988 when the mill was decommissioned. Since the early 1900's, much of the country's uranium ore was milled at this site. Radiological contamination of the ground water, soils, and facilities caused the US Environmental Protection Agency to consider this site a Superfund site regulated under the Comprehensive Environmental Response Compensation, Liability Act and the Resource Conservation and Recovery Act. Since 1988, the site facilities have been razed, contaminated soils removed, and contaminated ground water pumped to evaporation ponds. All contaminated materials have been placed on a mesa top at the Uravan site where liquid waste materials were sprayed. These materials will be capped in place. It is estimated that the remeditation process will take 17 years. Monitoring of contamination is an ongoing process. The Uravan Mill Site is located on the San Miguel River, tributary to the Dolores River. Old tailings ponds designed to leach extraction solutions to the ground water and river were replaced in the early 1990's with lined evaporation ponds. These old ponds leached highly toxic and radioactive materials to the ground water and the San Miguel River. Also, prior to reclamation, a pipeline carrying a brine solution followed the San Miguel and the Dolores river. Breaks in this pipe occurred often, resulting in a plume of highly saline solution released on nearby vegetation and into the river. This pipeline no longer exists. (Cudlip, L 1987 to 1997, pers. Obser., Bio- Environs).

Since remediation began, water quality samples and bioassays of aquatic organisms reveal low levels of radionuclides and metals. More interesting is the immediate increase of Simuliidae larvae (black fly larvae), a pollution tolerant organism, after increased sedimentation. Increased sedimentation in the past 10 years has been typically related to intensive work in the San Miguel River streambed to remove contaminated soils, to reconstruct the river channel, or to create wetlands (Cudlip, L 1987 to 1997, pers. Obser., Bio-Environs).

Contamination of the Colorado River prior to remediation of this mill site may have been possible, but is undocumented. More likely, contaminants associated with sediments flowing downstream from the site, settle along the San Miguel or Dolores River before reaching the Colorado River, and before reaching the parks. Regardless, remediation of the site was clearly mandated, and the project is nearing compleation.

Lisbon Valley

Copper mining may return to the Lisbon Valley near Canyonlands. On August 8, 1995 Summo USA Corporation submitted a proposed Plan of Operations to the Bureau of Land Management, Moab District to develop a copper mine in Lisbon Valley, east of the Canyonlands Needles District. A heap leach sulfuric acid process would be introduced to extract copper from formally milled tailings and from ore. In this process, ore is crushed, piled in a heap and then sprinkled with sulfuric acid. As the sulfuric acid filters through the pile it dissolves the copper. The solution is then pumped out, and the copper recovered. The proposal includes the development of 4 open pits to access copper ore; four waste dumps, crushing facilities; a 266 acre leaching pad; a processing plant and ponds to recover the ore; construction of a 10.8 mile powerline to the project site; and associated support facilities. The total disturbance would include 1,103 acres and be located on a combination of federal, state, and private lands. Mining and processing would occur for a ten year period, with reclamation taking an additional five years to complete (Bureau of Land Management, 1997).

Geologically, the area is a collapsed salt valley which drains into the Dolores River. The record of decision in the Environmental Impact Statement confirmed the project, but this record of decision was protested as a result of inadequate ground water data. Recently, data and models assessing the development of pit lakes and the leaching characteristics of the rock substrate confirmed earlier conclusions that the copper operations would not cause impacts to the surrounding aquifers (Adrian Brown, Inc., 1998) . The Annual Hydrogeologic Update (Adrian Brown, Inc., 1998) demonstrates through modeling that water collected in the pits would be significantly better than the intact Burro Canyon aquifer at the end of mining and for 45 to 69 years later. However, the combined effects of evaporation and shallow ground water flowing to the pits contribute to an increase in total dissolved solids (TDS) above those in the Burro Canyon Aquifer (2,039 mg/L total dissolved solids). The shallow ground water will not be affected by these pits because ground water will flow from the aquifer to the pits in the long term according to Adrian Brown (1998), the consulting firm which conducted the modeling.

A deeper aquifer, the N-aquifer, has total dissolved solids level of 273,177 mg/L. Contamination of this aquifer would not occur, but water quality will tend to improve for 90 to 110 years after mining due to delivery of relatively clean water from the pits to the deep aquifer. Eventually concentrated pit water could reach the deep aquifer and increase total dissolved solids in the aquifer from 3 percent to 7 percent, well below the 25 percent total dissolved solids limit increase allowed by the ground water quality protection regulations (Adrian Brown, 1998).

Trace metals are not expected to concentrate in the pit ponds. Adrian Brown, Inc. (1998), through field tests, suggests that trace metals would be attenuated through natural processes and would not appear to concentrate in solution. Sorption and other chemical processes may control the fate of trace metals in the system. All told, ground water in the Lisbon Valley area appears to move northeast towards the Dolores River, and a fault system literally blocks movement of ground water to the west where the Needles District is located.

Potash

The Texaco Gulf Potash Mine (also known as Texasgulf, Inc. and Texas Gulf Sulfur Inc.) located on the Colorado River at the town of Potash was operated to collect potash originally through a pillar and post technique. This technique involves cutting rooms into the underground area leaving a series of pillars. These pillars support the mine roof and control the flow of air. In a tragic accident part of the mine collapsed killing several humans. Following this disaster, deposits were mined via an evaporative process. In 1970, Texas Gulf Sulfur Inc. began filling the underground mine with ground water from drilled wells. While drilling one of the wells for ground water, several artesian aquifers were encountered. These artesians broke into the mine and flooded it by January, 1971 months before complete fill of the mine was anticipated. Since they could not control water from the artesians, all the wells had to be capped. Instead, Colorado River water was pumped into the mine, and the solution containing potash was brought to the surface, transferred into ponds and allowed to evaporate (Phillips, 1975). The evaporite consisted of potash (KCl) as well as large amounts of salt (NaCl). The salt was stockpiled, and its proximity next to the Colorado River raised the concern that leachates may reach the river.

In the last 3 or 4 years, through a process of solution with Colorado River water and evaporation, the salt is developed into a marketable product. The pile size has been reduced considerably by this technique (Barnett, J., 1998, pers. comm., Colorado Salinity Control Forum ). Presently, there are seven existing leases in the area and thirteen prospecting applications that have not been processed. If an entity were interested in mining the area, the Bureau of Land Management would guide the development of an Environmental Impact Statement (Jackson, L., pers. comm.., Bureau of Land Management). The Bureau of Land Management periodically sees increased interest in this area, but no serious mining plans have come to fruition.

Abandoned Mines

The number of prospecting hatches on topographic maps and actual mine adits found on the ground attest to the rich mining history within Arches and Canyonlands National Parks and outside their boundaries. Concerns associated with abandoned mines relate to elevated radiation levels emitted from the mines and contaminated mine drainage. The development of mines on the Colorado Plateau stems from the exploration for and mining of the nation's radioactive ores since 1900. Radium was used for medicinal purposes and in the production of luminescent dials. Vanadium was used in steel production, and beginning in 1943, uranium was mined for nuclear weapons and later during the mid-1960's, uranium was used for nuclear generation of electric power. Since the 1960's production of uranium has declined, but continues on a small scale (Burghardt, 1996).

Burghardt (1996) notes that there are no active mines on National Park Service lands in the Colorado Plateau, but the National Park Service inventory shows 44 abandoned radium or uranium sites in or immediately adjacent to National Park Service units. Reclamation of these mines was not required when many mines were opened; the responsible parties are long gone. Clean up or remediation of the sites comes under the auspices of the current land manager - typically the National Park Service, Bureau of Land Management or U.S. Forest Service.

In Canyonlands, Burghardt (1988) was instrumental in recommending the type of closure for ten mines in Lathrop Canyon. The mines were closed using cable nets in February 1989 (Burghardt, 1990). Six more mine openings were closed in 1996, and another five were closed in 1998. Inventories by park personnel and by Burghardt document several other mine opening sites. These include one site with two openings in Arches; these have been backfilled. In Canyonlands, there are 13 sites with 33 openings of which 16 portals have been closed. More importantly, there are numerous abandoned mine sites adjacent to both parks' boundaries, particularly in the Yellowcat Mining District north and east of Arches National Park.

Water contamination in these abandoned mines is evidenced by samples taken from the Lathrop Canyon Mines that were closed. Gross alpha, gross beta, and radium 226 exceeded state standards. Burghardt (1988) also expressed concern with trace elements in the mine waters and increases in contamination downstream of the mine openings. The data were insufficient to determine if the increases were due to the abandoned uranium mines.

The National Park Service, Geologic Resource Division, spearhead the effort to inventory abandoned mines, eliminate public hazards in and near mines, and rehabilitate natural resources as they relate to abandoned mine sites on park lands. However, more work could be accomplished on lands adjacent to the park where the proximity of the abandoned mine or drainage from the mine may impact park lands and water. A project statement is presented to this effect (ARCH-N-030.000, CANY-N-037.000).

Abandoned Oil and Gas Wells

A number of abandoned oil and gas wells exist within and close to park boundaries; they were used in the late 1970's and early 1980's to assess ground water quality for possible culinary water supply development (Sumsion and Bolke,1972; Richter, 1980; Hand, 1979) and to examine hydrology of the Needles District specific to a proposed nuclear waste facility east of Canyonlands (Ecosystems Research Institute, 1984). Sumsion and Bolke (1972) list three oil and gas wells in the northern part of Canyonlands. Developed by Husky Oil Co., Rosen Oil Co., and Pure Oil, there is information on the location, well depth, and geological formation associated with these wells. Ecosystems Research Institute (1984) also notes the Pure Oil well. Richter (1980) lists 29 petroleum test wells in the Needles District area and contiguous lands. Richer (1980) provided information on each well's location, depth to source, depth to production zone, reported rate of production, and reported water quality. Of these 29, 13 produced saline waters. Hand (1979) listed five petroleum test wells in the Maze District one of which produced saline waters, and two where water quality was unknown. Those parameters noted in Richter (1980) were also listed in Hand (1979). It is not known whether these wells were developed or were capped. Also there is no information regarding petroleum test wells in Arches.

Some of the geologic formations in the region were crated in marine environments and therefore have a naturally high concentration of dissolved solids. Fossil fuels are generally associated with marine shales and extraction of these resources results in increased dissolution of soluble minerals. Development of petroleum test wells can result in the discharge of saline ground water. Old well casings may corrode resulting in a release of saline water into the well. These wells were drilled in many cases over thirty years ago. No recent information regarding these wells has been found that may indicate disturbance, and the Bureau of Land Management requires that abandoned wells be plugged. However, the park needs to assess the status of the wells and any other petroleum test wells that may be present. A project statement addresses the need to inventory abandoned gas and oil wells. (ARCH-N-030.000, CANY-N-037.000).

Existing Mines and Oil and Gas Operations

There are approximately 31 active mines, mostly uranium mines within Grand, San Juan, Garfield, and Wayne counties that the Utah Division of Oil, Gas and Mining have recorded. This number does not include a State Institutional and Trust Lands inventory nor leases on private lands. Mining in the vicinity of Canyonlands and Arches may present potential impacts to water resources within the parks. A substantial amount of uranium mining in areas surrounding the National Park Servicelands on the Colorado Plateau has occurred in the past. Ground surface disturbance leading to erosion can impact water resources. Surface runoff and pollution from uranium mines can result in elevated levels of heavy metals, radionuclides and other toxic elements. Explortaion of oil and gas can result in the release of highly saline waters, because many of the wells reach geologic formations created in marine environments. In cases where drilling techniques do not meet approved protocols, drilling into or through these formations may cause contamination of less saline water in other formations (Aubry, A., 1998 pers. comm., Bureau of Land Management).

Several people at the September 18, 1997 scoping meeting expressed interest in an inventory of active mineral mines and oil and gas leases. To that end, a project statement is presented. (ARCH-N-030.000, CANY-N-037.000).

Source National Park Service, Water Resources Division

cover of GRE report

Geologic Resource Evaluation Report – A detailed geologic report is available that provides an introduction to the geologic history of the park and its geologic formations, identifies geologic features and processes that are important to park ecosystems, describes key resource management challenges and possible solutions, and lists geologic research and monitoring needs.

References

Adrian Brown. 1998. Project Annual Update of the Lisbon Valley Hydrogeologic System Evaluation Vol. 1. Summo USA Corporation, Denver , CO .

Aubry, A. 1998. Personal communication. Bureau of Land Management, Moab , UT.

Baars, D. L. 1972. The Colorado Plateau. University of New Mexico Press, Albuquerque , NM .

Barnett, J. 1998 Personal communication. Colorado River Salinity Forum, Salt Lake City , UT.

Barth, R. C. and E.J. McCullough. 1988. Livestock grazing

Berghoff, K. and D. Vana-Miller. 1997. Canyonlands National Park , Arches National Park , and Natural Bridges National Monument Water Resources Scoping Report. NPS Water Resources Scoping Report. NPS/NRWRS/NRTR-97/94.

Bureau of Land Management. 1997. Final Environmental Impact Statement Lisbon Valley Copper Project, Moab District , Moab , UT

Ecosystems Research Institute. 1984. Water resources assessment Canyonlands National Park , - Needles District and adjacent BLM lands, Volume I. Ecosystem Research Institute. , Logan , UT.

Hand, F.E. 1979. Groundwater resources in the northern part of Glen Canyon national Recreation Area and adjacent lands west of the Colorado and Green rivers, Utah . University of Wyoming, Water Resources Research Institute, Dept. of Geology, Laramie , WY

Irwin, R. 1997. Personal communication. National Park Service, Fort Collins, CO.

Kennedy, C.E. 1977. Wildlife conflicts in riparian management: water. Pp. 52-58. In Importance , Preservation and Management of Riparian Habitats. USDA Forest Service General Technical Report RM-43.

Knopf, F.L. and R.W Cannon. 1981. Structural resilience of a willow riparian community to changes in grazing practices. In Decline of Riparian Communities in a Portion of Southwestern Wyoming . Range Improvement Notes. D.A. Shute, Editor. U.S. Forest service Intermountain Region.

Lammars, D.A. 1991. Soil Survey of Canyonlands Area , Utah , Parts of Grand and San Juan Counties . USDA, Soil Conservation Service.

Long, B.A. and R.A. Smith. 1996. Water Quality Data Analysis and Interpretation for Spring monitoring sites : Southeast Utah Group. Technical Report. National Park Service. NPS/NRWRD/NRTR-96/77.

Parker, R.S. and J.M. Norris. 1983. Simulated Effects of Anticipated Coal Mining on Dissolved Solids in Selected Tributaries of the Yampa River , Northwestern Colorado . USGS, Water Resources Investigation Report 83-4084, Lakewood , CO .

Phillips, M. 1975. Cane Creek Mine solution mining project, Moab Potash Operations, Texasgulf, Inc., In J.E. Fassett and S.A. Wengerd, eds., Canyonlands Country: Four Corners Geological Society 8' h Guidebook.

Richter, Jr., H. R. 1980. Ground water resources in the part of Canyonlands National Park east of the Colorado River and contiguous Bureau of Land Management Lands, UT , MS U. of Wyoming.

Sumsion, C.T. 1971. Hydrologic investigations in Arches National Monument . USGS, Salt Lake City , UT.

Sumsion, C.T. and E.. Bolke. 1972. Water resources of part of Canyonlands National Park , Southeastern Utah , U.S. Geologic Survey. Salt Lake City , Utah .

US Nuclear Regulatory Commission. 1996a. Draft Environmental Impact Report Related to Reclamation of the Uranium Mill Tailings at the Atlas Site , Moab , Utah . Source Material License No. SUA 917, Docket No. 40-3453, Atlas Corporation, NUREG-1531.

US Nuclear Regulatory Commission. 1996b. Draft Technical Evaluation Report for the proposed revised reclamation plan for the Atlas Corporation Moab Mill. Source Material License No. SUA 917, Docket No. 40-3453, Atlas Corporation, NUREG-1532.

US Nuclear Regulatory Commission. 1997. Final Technical Evaluation Report for the proposed revised reclamation plan for the Atlas Corporation Moab Mill. Source Material License No. SUA 917, Docket No. 40-3453, Atlas Corporation, NUREG-1532

The Greatest Density of Arches in the World
Wind and water, extreme temperatures, and underground salt movement are responsible for the sculptured rock scenery of Arches National Park. On blue-sky days, it is hard to imagine such violent forces - or 100 million years of erosion of sandstone - creating this land that boasts the greatest density of natural arches in the world. The more than 1,500 cataloged arches range in size from a 3-foot opening (the minimum considered an arch) to Landscape Arch, which measures 306 feet from base to base. All stages of decay and arch formation are found here. In 1991 a slab of rock about 60 feet long, 11 feet wide, and 4.5 feet thick fell from the underside of Landscape Arch leaving behind an even thinner ribbon of rock. Delicate Arch, an isolated remnant of a bygone fin, stands on the brink of a canyon, with the dramatic La Sal Mountains for a backdrop. Spires, pinnacles, and balanced rocks perched atop seemingly inadequate bases vie with the arches as scenic spectacles.

Arches National Park lies in southeastern Utah's red rock country. For a short stretch the Colorado River borders the park. A bridge on U.S. Highway 191 connects the park with Moab, Utah. Near this bridge users of the Old Spanish Trail swam mules across in the 1830s. A remnant of the trail adds historical intrigue to Arches. So does Wolfe Ranch, the remains of a typical early-West cattle operation.

The Geologic Story
The national park lies atop an underground salt bed, which is basically responsible for the arches and spires, balanced rocks, sandstone fins, and eroded monoliths that make the area a sightseer's mecca. Thousands of feet thick in places, this salt bed was deposited over the Colorado Plateau some 300 million years ago when a sea flowed into the region and eventually evaporated. Over millions of years, the salt bed was covered with residue from floods and winds and the oceans that came in intervals. Much of this debris was compressed into rock. At one time this overlying earth may have been one mile thick.

Salt under pressure is unstable, and the salt bed below Arches was no match for the weight of this thick cover of rock. Under such pressure it shifted, buckled, liquified, and repositioned itself, thrusting the Earth layers upward into domes. Whole sections dropped into cavities. In places they turned almost on edge. Faults occurred. The result of one such 2,500-foot displacement, the Moab Fault, is seen from the visitor center.

As this subsurface movement of salt shaped the Earth, surface erosion stripped away the younger rock layers. geologic contact Except for isolated remnants, the major formations visible in the park today are the salmon-colored Entrada Sandstone (top, photo at left), in which most of the arches form, and the buff-colored Navajo Sandstone (bottom, photo at left). These are visible in layer cake fashion throughout most of the park. Over time water seeped into the superficial cracks, joints, and folds of these layers. Ice formed in the fissures, expanding and putting pressure on surrounding rock, breaking off bits and pieces. Winds later cleaned out the loose particles. A series of free-standing fins remained. Wind and water attacked these fins until, in some, the cementing material gave way and chunks of rock tumbled out. Many damaged fins collapsed. Others, with the right degree of hardness and balance, survived despite their missing sections. These became the famous arches. This is the geologic story of Arches - probably. The evidence is largely circumstantial.

How Are Arches Formed?
formation of arches

  1. As the Earth upwarped here, deep cracks penetrated to the buried sandstone layer.

  2. Erosion wore away exposed rock layers and enlarged the surface cracks, isolating narrow sandstone walls, or fins. Alternating frosts and thawing caused

  3. crumbling and flaking of the porous sandstone and eventually cut through some of the fins.

  4. The resulting holes were enlarged to arch proportions by rockfalls and weathering. Arches eventually collapse, leaving only buttresses that in time will erode. Some natural bridges may look like arches, but they form in the path of streams that wear away and penetrate the rock. (Natural Bridges National Monument is a superb place to view these bridges). Pothole arches form by chemical weathering as water collects in natural depressions and eventually cuts through to the layer below.



park maps subheading

The General park map handed out at the visitor center is available on the park's map webpage.

View the park's map to create your own personal maps and images right here.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

photo album subheading

A geology photo album can be found on the park's website.

For information on other photo collections featuring National Park geology, please see the Image Sources page.

books, videos, cds subheading

Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.

Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.



geologic research subheading

 

For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.

The NPS maintains a searchable data base of research needs that have been identified by parks.

A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.



selected links subheading

NPS Geology and Soils Partners

NRCS logoAssociation of American State Geologists
NRCS logoGeological Society of America
NRCS logoNatural Resource Conservation Service - Soils
USGS logo U.S. Geological Survey

teacher feature subheading

Currently, we do not have a listing for any park-specific geology education programs or activities.

General information about the park's education and intrepretive programs is available on the park's education webpage.

For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.
updated on 01/04/2005  I   http://www2.nature.nps.gov/geology/parks/arch/index.cfm   I  Email: Webmaster
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